Road surfacing composition and a process for preparing same



United States Patent ROAD SURFACING COMPOSITION AND A PROCESS FOR PREPARING SAME Clarence P. Munding, Santa Maria, Calif.

No Drawing. Application January 30, 1957 Serial No. 637,092

5 Claims. '(Cl. 106 -278) This invention relates to an improved road surfacing composition and particularly to asphalt type surfacing materials and a process for preparing the same.

One of the principal objects of this invention is to provide a road surfacing composition which appreciably increases the service life of standard vehicle tires operating over such surface.

A further object of this invention is to provide a road surfacing composition which may be mixed at temperatures below those normally used with known gravelasphalt surfacing materials.

A more particular object of this invention is to provide an economical road surfacing composition comprising diatomaceous shale and oil and a method of mixing same.

Other objects and advantages will be apparent, it is believed, from the following detailed description of the materials and process used in a preferred embodiment of the present invention.

Common asphalt type road-surfacing materials are formed by mixing sand and rock gravel with an asphalt base crude oil at temperatures in the range of 375 to 450 F. The resulting road surface is relatively stable and insensitive to normal temperature fluctuation. However, the type of gravel used causes tires, particularly those used on heavily laden trucks, to wear more rapidly, reducing the service life below that expected on more ideal road surfaces.

In accordance with the present invention, a material has been discovered which, when mixed with an asphalt base emulsion oil, results in a road surfacing material which is smoother and less abrasive than common asphalt materials.

The material is a gravel formed from an oil impregnated diatomaceous shale and particularly such a shale as is found eight miles southwest of the city of Santa Maria, county of Santa Barbara, in the State of California in a region known as Shuman Cut. This shale in the untreated condition contains approximately 35 gallons of crude oil per ton.

In preparing the composition which is the subject of this invention, oil-impregnated diatomaceous shale isi introduced into a standard rock crusher and is pulverized to the size of pea gravel. Pea gravel as used herein is defined as gravel, the particles of which have diameters between one-quarter and one-eighth of an inch. In the process of pulverizing, some of the shale is reduced to dust-i. e., particles having a maximum diameter of less than one-eighth inch. Particles having diameters greater than one-quarter inch are screened out and recycled through the pulverizer. The dust and pea gravel are separated by screening.

After pulverizing and screening, thepea gravel and dust are mixed. The proportions of pea gravel to dust should be in the range of 35 to parts by weight pea gravel to to 45 parts by weight dust. It has been found that the most satisfactory road surfacing mate- 2,877,127 Patented Mar. 10,- 1959 ICC rial is obtained when the by weight ratio is 40 parts pea gravel to 60 parts dust. In addition, although pea gravel is the preferred size, particles having a diameter greater than one-quarter inch may be incorporated in the final composition, However, these larger particles reduce the binding effect of the asphalt and are not preferred.

The gravel portion as described above is then mixed with a high viscosity asphaltbase emulsion ,oil such as is commonly used in asphalt type road surfaces. The proportions of gravel to oil should be in the range of from 35 to 50 parts by volume of the gravel to 7.5 to 15 parts by volume of oil. It has been discovered that the most satisfactory mixture may be obtained with 40 parts gravel to 10 parts oil. The gravel and oil are mixed in a rotating drum, either in individual batches or in a continuous feed system such as is commonly used in mixing standard gravel asphalts. The mixing temperature should be between 200 and 300 F., the optimum temperature being 250 F. At temperatures below 200 F. the oil does not penetrate the shale while at temperatures above 300" F. the materials are burned or scorched. Mixing of the gravel and oil at the temperatures specified is continued until the composition becomes fluffy. The normal mixing time is 10 to 30 minutes, depending on the mixing temperature. When mixing is completed, a substantially homogeneous composition results, having a density of approximately 1,300 pounds per cubic yard. This composition may then be spread on a prepared grading and pressed or compacted to form a suitable road surface. The composition will startto compact as pressure is applied and the hardness of the resulting road surface may be increased by increasing the pressure. If desired, the composition may be cooled to ambient temperature and will retain its fiuffy characteristic. The composition may then be reheated, spread and pressure applied to compact it to form the desired road surface. Since the composition does not tend to set, it can be premixed and transported to the area on which it is to be used.

The resulting asphalt road. surface. is smooth and less abrasive than standard asphalt surfaces thereby reducing tire wear and road noise. Since the mixing temperature is between and 200 F. below that used in mixing normal gravel asphalts, the material is easier to prepare and handle. Finally, the surface life of such a road surface is equivalent to that of standard gravel asphalt surfaces.

The following is a specific example of a preferred process of forming the road surfacing composition which is the subject ,of the invention.

Oil impregnated diatomaceous shale having the followmg composition:

and obtained from the Shuman Cut region in the county of Santa Barbara, State of California was introduced into a standard rock crusher, adjusted so as to reduce the particle size of the shale to approximately one-quarter to one-eighth of an inch. As therock was discharged from the crusher it passed through a one-quarter inch shaker screen, .the unpassed particles having diameters greater than one-quarter of an inch being recycled through 3 the crusher. .A-gfurtherscreen was provided whichseperated the .dust;from the pea gravel.

Asphalt base crude oil having a viscosity at 210 F. of from 300 to 450 centiposes and being not more than 12 gravity A. P. I. andan'average of-9.gra,vity A. P. l. was preheated 'to200 .F. and -a mixing :drum preheated to 250 F. Into -the preheated rotating drum which had a capacity of approximately 20,000 gallons was introduced 8 cubic yards of the pea graveland 12 cubic yards of the dust, resulting-from the crushing operation. To this gravel mixture was added 1,000 gallons of the preheated asphalt base crude oil at a rate of 100 gallons a minute. Mixing was continued for 25 minutes, the temperature of the mixture raised to 250 F. and the composition discharged from the drum. The resulting composition was a homogeneous fiuify'material having a density of approximately 1,300 pounds per cubic yard.

Ten cubic yards of 'this material was set aside and allowed to cool. The remaining material, approximately l cubic yards, was spread on a prepared and graded road bed to form a layer approximately one inch thick and compressed with a heavy roller to a thickness of approximately one-half inch. The application of pressure caused the composition'to compact and a smooth, hard road surface was achieved. The cubic yards of the composition which had been set aside was allowed to cool to ambient temperature. "The cool material retained the tiufiy characteristic and same density as that found in the original mixed material. The cooled composition was then heated to 200 F., spread and compressed in the manner above described. The resulting road surface was equivalent of that obtainedfrom the previous surfacing.

Tire wear tests .were made on the resulting road surface and compared to similar tests made on standard surfaces. The results of these tests showed that tire wear was appreciably reduced. For example, a two axle dump truck with a seven ton payload was operated on level hard surfaces consisting of black-top and concrete. The lives of new tires were found to be as follows:

Front axle 13,000 miles per set of 2 tires,

Cost $00969 per tire per mile;

Rear axle 15,000 miles per set of 4 tires, Cost $0084 per time per 'mile;

an average cost of $00883 per tire per mile. A second two axle dump truck with a seven ton payload was operated over hilly roads surfaced with a diatomaceous shale composition. The lives of new tires operated on this surfaces were found to be as follows:

Front axle 35,000 miles per set of 2 tires,

Cost-$0036 per tire per mile;

Rear axle 35,000 miles .per -set of :4 tires,

Cost $0036 per tire permile;

.less than that of standard asphalt base surfaces.

Having fully described myinvention, it is to be understood that I do not wish to be limited to the precise details of the examples set forth but my invention is of the full scope of the appendediclaims.

I claim:

1. A road surfacing composition comprising: a homogeneous mixture of four parts by volume crushed oil bearing'diatomaceous shale ;and.one part byvolume high viscosity asphalt base crude oil, the size of the particles msai shale. being substant al pea-craw atlds ltst- 2. A road surfacing composition comprising: a homo geneous mixture of four parts by volume crushed oil bearing diatomaceous shale, said shale analyzing:

Percent Silica 71.88 Iron oxide 3.42 Alumina 13.42 Calcium oxide 7 1.64 Magnesium oxide Q 1.72 Sulfur trioxide V 1.64 Sodium oxide 2.30 Potassium oxide y H p I 1.28 Crude oil 2.70

the sizes of the particles in said shale being substantially pea gravelzanddust; the by weight ratio of pea gravel to dust in said mixture being approximately 40:60; and one part'by volume high viscosity asphalt base crude oil, said crude oil having a viscosity'at 210 F. offrom 300 to450 centipoise and being not more than 12 gravity A. P. I. w 3. A process for preparing a roadsurfacing composition comprising: mixing four parts by volume-of a crushed oil bearing diatomaceous'shale with one part by volume high viscosity asphalt basecrude oil ata temperature range of from 200 F. to 300 F. to'forma homogeneous mixture, the --sizes.of the particles in said shale being substantially pea gravel and dust.

v4. Aprocess for preparing a road surfacing composition comprising: mixing four parts by volume of a crushed oil bearing diatomaceous shale, said shale analyzing:

'Percent Silica 71.88 Iron oxide 3.42 Alumina 13.42 Calcium oxide 1.64 Magnesium oxide .4- 1.72 Sulfur trioxide 1.64 Sodium oxide 2.30 Potassium oxide 1.28 Crude oil 2.70

shale, said shale analyzing:

Percent Silica 71.88 Iron oxide 3.42 Alumina I I 13.42 Calcium oxide 1.64 Magnesium oxide -i 1.72 Sulfur trioxide 1.64 Sodium oxide 2.30 Potassium oxide 1.28 Crude oil 2.70

mixture, combining said shale mixture with one part by volume high viscosity asphalt base crude oil, said crude oil having a viscosity at 210 F. of from 300 to 450 centi- 5 poises and being not more than 12 gravity A. P. I. at a 743,051 temperature from 200 F. to 300 F. to form a homoge- 1,235,989 neous composition.

References Cited in the file of this patent 5 2 772 UNITED STATES PATENTS 505,531 McCook Sept. 26, 1893 6 Amies Nov. 3, 1903 Mertens Aug. 7, 1917 FOREIGN PATENTS Great Britain of 1871 

1. A ROAD SURFACING COMPOSITION COMPRISING: A HOMOGENEOUS MIXTURE OF FOUR PARTS BY VOLUME CRUSHED OIL BEARING DIATOMACEOUS SHALE AND ONE PART BY VOLUME HIGH VISCOSITY ASPHALT BASE CRUDE OIL, THE SIZE OF THE PARTICLES IN SAID SHALE BEING SUBSTANTIALLY PEA GRAVEL AND DUST. 